Parameters Affecting the Loading Behavior and Degradation of Electrically Active Filter Materials

Abstract

Electrically active fibrous filters, that is fibrous filters whose fibers carry a permanent electric charge, are a popular alternative to conventional fibrous filters in applications where low pressure drop and high collection efficiencies are critical. The advantage of these materials is the additional collection efficiency, due to electrostatic mechanisms, that can be achieved without pressure drop increase. Although the efficiency of these materials is always superior to that of a conventional material of similar structure, the efficiency of these materials can fall as they are loaded with particles, so it is necessary that a proper account be taken of this process during use. Significant advances have been made in understanding the mechanisms responsible for this reduction in efficiency in a recent experimental study of the loading behavior of a mixed fiber type electrically active material. This study has identified a number of parameters that cause the filtration efficiency to be reduced, and in so doing also has allowed an empirical equation to estimate the maximum penetration through the material over the course of its life to be elucidated. Furthermore, a series of experiments designed to investigate the effects of particle size and particle charge on filter degradation has been performed that prove conclusively that the reduction in filtration efficiency of this material during loading is not a charge neutralization process.